Electron Configurations

• Explains how electrons are distributeddistributed among an atom’s orbitals

• Each part identifies part of an electron’s “address,address,” or location,within an atom

• Example: 1s2 is the electron configuration for helium- 11 is the highest energy level helium in which He

places electronselectrons in the ground state- ss is the typetype of orbital in which the electrons are being placed (called sublevels)- 22 is the numbernumber of electrons found in that orbital

Principal Energy Levels• 77 principal energy levels - one correlating to each

periodperiod (row) on the periodic table• Each level requires an increase increase in energy for

electrons to be placed there

• each principal energy level has its own number of sublevelssublevels (describes shapeshape of orbitals)

Sublevels

- s sublevel: spherical (groups 1 and 2)- p sublevels: dumbbells

(groups 13 - 18)- d sublevels

(transition metals)- f sublevels

(lanthanides & actinides)

Atomic Orbitals

Atomic Orbitals• Each sublevel

contains a different numbernumber of orbitals

• Orbitals are regionsregions where electrons are most likelylikely to be found in an atom

- ss sublevel has 11 orbital- pp sublevel has 33 orbitals - dd sublevel has 55 orbitals- ff sublevel has 77 orbitals

Atomic Orbitals

Each orbital holds only 2 electrons

Electron Configuration Rules

• Aufbau’s rule: electrons are placed in orbitals of lowest energy first- ground state: lowest energy level occupied by an

electron - excited state: any level above the ground state in

which an atom’s electron is found

• Hund’s rule: when electrons enter orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with the same spin

• Pauli’s exclusion principle: each orbital can hold a maximum of two electrons with opposite spin

Sublevels & Periodic Table

Valence Electrons- elements in the same groupgroup react in a similar manner- they share similar reactions because they have the same number of valencevalence electrons- valence electrons are the electrons in the outermost outermost energy level

Atom/Ion

OrbitalDiagram

ElectronConfiguration

H

1 electron1s 1s1

1 UPE 1 VE

Atom/Ion

OrbitalDiagram

ElectronConfiguration

Be

4 electrons1s 1s22s22s

0 UPE 2 VE

Atom/Ion

OrbitalDiagram

ElectronConfiguration

B

5 electrons1s 1s22s22p12s 2p

1 UPE 3 VE’s

Atom/Ion

OrbitalDiagram

ElectronConfiguration

O

8 electrons1s 1s22s22p42s 2p

2 UPE’s 6 VE’s

Atom/Ion

OrbitalDiagram

ElectronConfiguration

Ne

10 electrons1s 1s22s22p62s 2p

0 UPE’s 8 VE’s

Atom/Ion

OrbitalDiagram

ElectronConfiguration

Mg

12 electrons1s 1s22s22p63s22s 2p 3s

0 UPE 2 VE

Atom/Ion

OrbitalDiagram

ElectronConfiguration

Cl

17 electrons

1s1s22s22p63s23p5

2s 2p 3s

1 UPE 7 VE

3p

• How many electrons can be placed into the 2p orbitals?

A. 6B. 2C. 4D. 8

• How many electrons can be placed in the third energy level?

A. 6B. 10C. 18D. 24

• How many sublevels are there in the fourth energy level?

A. 2B. 3C. 5D. 7

• How many electrons can be placed in the 4f sublevel?

A. 6B. 2C. 10D. 14

Noble Gas Shortcut• The Noble Gas shortcut can be used to represent

the electron configuration for atoms with many electrons. Noble gases have a full s and p and therefore can be used to represent the inner shell electrons of larger atoms.

• Lead:• Write the electron configuration for Xenon:

• Substitution can be used:• Manganese• Arsenic• Promethium

Ion Charges• Metals lose electrons (forming cations) in

order to have the same electron configuration as the nearest noble gas (very stable; typically 8 valence electrons

• Nonmetals gain electrons (forming anions) in order to have the same electron configuration as the nearest noble gas

GroupGeneral Electron

Configuration

Number of Valence

Electrons in Atom

Charge

1 (alkali metals) s1

2 (alkaline earth metals)

s2

13 s2p1

14 s2p2

15 s2p3

16 s2p4

17 (halogens) s2p5

18(noble gases)

s2p6

11 +1+1

22 +2+2

33 +3 (Al, Ga)+3 (Al, Ga)44 -4-455 -3-366 -2-277 -1-1

2 (He)2 (He)8 (all others)8 (all others)

00

What charge would an aluminum (Al) ion have?A.+1 B. +3 C. -3 D. -5

What charge would an iodine (I) ion have?A.+1 B. -2 C. -1 D. 0

What charge would a strontium (Sr) ion have?A.+1 B. +3 C. -3 D. -5

What charge would a nitrogen (N) ion have?A. +1 B. +3 C. -3 D. +5